E

Note that e33 ^ 0 even though s33 = 0 (i.e., a biaxial state of stress gives rise to a triaxial state of strain) because of the Poisson's effect. 2. Plane strain condition. If the strain is negligible in the x3 (or z) direction, plane strain condition implies that e33 = e23 = e13 = 0. Substituting this condition into Equation 1.31, we have